METHODS OF ANALYSIS 59 



which is a modification of Low's method: Dissolve ^ gram of the 

 sample in 10 cc. nitric acid. When in solution, dilute with cold 

 water and add sodium carbonate until the solution is alkaline, 

 make acid with acetic acid and add about 3 grams potassium iodide 

 and some starch solution. Titrate with a sodium thio-sulphate so- 

 lution which has been standardized with pure copper. 



Oxidize the filtrate from the copper sulphide thrown down by 

 the thio-sulphate as described above, with nitric acid and potas- 

 sium chlorate and evaporate until the volume is about 300 cc. 

 Make a basic acetate separation and determine iron or alumina by 

 the well-known methods. Make the filtrate from the iron or 

 alumina strongly alkaline with ammonia, heat to boiling and add 

 ammonium persulphate, boil for five minutes, filter, and wash 

 with hot water, burn, and weigh as Mn,0 4 . 



To the filtrate from the manganese add ammonium phosphate 

 in excess, heat to boiling and add hydrochloric acid until there is 

 but a slight excess of ammonia, boil for five minutes, filter, and 

 wash with hot water. The ppt. may be dried and weighed as 

 ZnNH 4 P0 4 , or it may be filtered on a Gooch crucible and ignited 

 to Zn 2 P 2 7 . It may also be titrated with a standard acid and al- 

 kali. 



Any nickel which may be present will be found in the filtrate 

 from the zinc, and may be ppt. as sulphide and ignited to MO. 



If manganese is present in small quantities, it may be deter- 

 mined in a separate portion by the following method: Weigh 0.2 

 gram of the sample into a suitable test tube, add 10 cc. nitric acid 

 (Sp. Gr. 1.20), and warm until the sample is dissolved and all ni- 

 trous fumes are driven off. Add 15 cc. silver nitrate solution (1.33 

 grams of the salt to 1 litre of water) and about ^ gram of ammo- 

 nium per-sulphate, warm until the manganese is oxidized to per- 

 manganic acid, cool, transfer to a beaker, dilute to 100 cc. and 

 titrate with standard sodium arsenite or hydrogen peroxide until 

 disappearance of the pink color. 



DETERMINATION OF PHOSPHORUS. 



To determine phosphorus, dissolve 1 gram of the sample in 5 

 cc. fuming nitric acid, evaporate to expel most of the free acid, add 

 10 cc. cone. HC1 and water, heat to boiling and ppt. the lead, tin 

 and copper with metallic zinc, filter and wash with hot water. To 

 the filtrate add some iron solution free from phosphorus and 10 cc. 



